The present exemplary embodiment relates to generally to fusing of images in a printing system including a plurality of marking engines. It finds particular application in conjunction with a printing system in which images generated by two or more marking engines are destined to be assembled into the same document. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
In a typical xerographic marking engine, such as a copier or printer, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to a print medium, such as a sheet of paper. The fusing of the toner onto the paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure. The fusing operation serves both to fix the image to the paper and also to impart gloss. In general, higher fuser roll temperatures pressures and longer dwell times are associated with higher gloss levels. For color printing, high gloss levels are often desired and thus fusers are generally run at well above the minimum temperature for achieving adequate fix.
Systems which incorporate several small marking engines have recently been developed. These systems enable high overall outputs to be achieved by printing portions of the same document on multiple marking engines. Such systems are commonly referred to as “tandem engine” printers, “parallel” printers, or “cluster printing” systems (in which an electronic print job may be split up for distributed higher productivity printing by different marking engines, such as separate printing of the color and monochrome pages). Such integrated printing systems have multiple fusers since each marking engine incorporates the fuser or fusers appropriate for fusing the images applied by that particular marking engine.
In some multiple marking engine systems, a process known as “tandem duplex printing” is employed. In this process, a first marking engine applies an image to a first side of a sheet and a second marking engine applies an image to a second side of the sheet. Each of the marking engines is thus operating in a simplex mode to generate a duplex print. As a result, a finished document, when assembled, may include images generated by two or more marking engines. The eye is particularly sensitive to any variations in gloss between images when these are in a side-by-side relationship.
Although nominally equivalent, marking engines may provide different levels of gloss. Indeed the gloss level of a marking engine may vary over the course of a day, depending on the use of the marking engine.